Effect of reaction time on free radical concentration in hydrogenation liquefaction of Naomaohu coal

Coal from Naomaohu (NMH) in Xinjiang as raw material, hydroliquefaction experiments were performed in a batch high-pressure liquefaction reactor. Variations of free radical concentration of PAA and the intermediate products of hydroliquefaction with reaction residence time were examined with an EPR spectrometer. The results show that conversion rate of NMH coal hydroliquefaction first rises and then decreases. The maximum conversion rate and oil yield is 96.87% and 53.01% in 60 min. The free radical concentration of NMH is 2.6654×10¹⁸/g. PAA's free radical concentration ranges between 1.2519×10¹⁸/g and 1.9121×10¹⁸/g, which first increases and then decreases with increasing reaction time. As for the intermediate products, PAA, its free radical concentration could reflect extent of hydroliquefaction reaction, which has the same variation tendency with the oil yield. PAA's g value is between 2.00301 and 2.00403, which is lower than that of NMH (2.00434). In the process of hydroliquefaction, its g value first rises and then decreases, which is closely related with the heteroatom content of N, S, O in PAA and is consistent with the element analysis result.